The present invention relates to an airbag for protecting an occupant as a result of expanding during an emergency in a vehicle.
In order to protect an occupant during a collision in a vehicle, a driver airbag device, a passenger airbag device, a back-seat airbag device, and a side airbag device are used. Of these various types of airbag devices, the passenger airbag device is accommodated inside an instrument panel disposed at the front side of the vehicle. Of the different types of passenger airbag devices, the type of passenger airbag device which is disposed at a windshield-opposing location of the top portion of the instrument panel is called a top-dash-mount-type passenger airbag device.
Hereunder, a description of an airbag device will be given taking a top-dash-mount-type passenger airbag device as an example.
FIG. 14(A) is a schematic side view used to illustrate the form of a conventional passenger airbag device when it has finished spreading. FIG. 14(B) is a front view thereof.
FIG. 15(A) is a schematic side view used to illustrate the form of the conventional passenger airbag device when a load acts thereupon (that is, when an occupant moves forward). FIG. 15(B) is a front view thereof.
FIG. 16(A) is a perspective view showing the conventional airbag in an expanded state. FIG. 16(B) is a perspective view showing the airbag in a squashed state when a load acts thereupon. FIGS. 16(C) and 16(D) are schematic views used to illustrate the characteristics of the squashed state of the airbag when a load acts thereupon.
The passenger airbag device shown in FIGS. 14(A) and 15(A) comprises a retainer R disposed at a windshield-F-opposing location of the top portion of an instrument panel P of a vehicle. Inside the retainer R are disposed an airbag 103 and an inflator I for supplying spread gas into the interior of the airbag 103. As simply shown in FIG. 16(A), the airbag 103 is a three-piece bag in which two pieces of side cloths 103b are sewed, one at each side of one piece of strip-like central cloth 103a interposed therebetween. The airbag 103 has an open end (that is, a gas-circulation hole) 103c which is narrowed down thinly at the base of the airbag 103. The open end 103c merges with a space in the inflator I. The airbag 103 is accommodated in a folded state inside the retainer R.
A description of the operation of the passenger airbag device will now be given.
At the time of a collision of a vehicle, spread gas is supplied into the airbag 103 from the inflator I. This causes the airbag 103 to expand in front of an occupant H, as shown in FIGS. 14(A) and 14(B). When the spreading of the airbag 103 is completed, the side cloths 103b extend in smooth curved forms or substantially straight lines from top to bottom portions thereof, as shown in FIG. 14(B). Here, the internal pressure or resistance inside the airbag 103 is substantially uniform at the top and bottom portions thereof.
After the airbag 103 has spread, as shown in FIG. 15(A), the occupant H that moves forward due to inertial force hits the airbag 103. This causes the airbag 103 to be pushed and squashed as a result of being sandwiched between the instrument panel P and the windshield F and the occupant H. At this time, as shown in FIG. 15(B), the upper portion of the airbag 103 spreads horizontally by a greater amount than the lower portion thereof. The following factors (1) to (3) cause the airbag 103 to be in a squashed state.
(1) As simply shown in FIG. 15(B), regarding the areas of the portions of the upper part of the body (from the waist upward) of the occupant H that hits the airbag 103, the area of the upper portion of the upper body (from the neck upwards) is smaller than the area of the lower portion of the upper body (from the shoulders downward).
(2) Regarding the masses of the portions of the upper body of the occupant H, the mass of the upper portion of the upper body is smaller than that of the lower portion of the upper body.
(3) While the lower portion of the airbag 103 is pushed upward by the knees of the occupant H, the upper portion of the airbag 103 is relatively not pushed.
When an attempt is made to correct the characteristics of the squashed state of the airbag 103, the output of the inflator I must be set relatively high.
A description of the resistance on the airbag 103 when a load is exerted thereupon will now be given with reference to FIG. 16.
When the occupant hits the airbag 103 shown in FIG. 16(A) from the front surface of the airbag 103, an external force a shown in FIG. 16(B) acts upon the airbag 103. As shown in the same figure, this causes the airbag 103 to become squashed while spreading flatly. Here, as shown schematically in FIGS. 16(C) and 16(D), the airbag 103 escapes towards a region of lower resistance (that is, in the directions of empty arrows inside the bag 103), so that the resistance against a load body f becomes smaller, thereby making it easier to squash the bag.
In view of the above-described problems, it is an object of the present invention to provide an airbag which has a more preferable spread form without increasing the output of an inflator.
To overcome the above-described problems, according to the present invention, there is provided an airbag for protecting an occupant as a result of expanding during an emergency in a vehicle, wherein, in a front form of the airbag at the time of expansion thereof as viewed from the occupant, an inwardly extending depression is formed in a middle portion of a side surface of the airbag as viewed in a vertical direction.
When the occupant collides against the airbag, the depression at the middle portion of the airbag makes it difficult for the gas in the bottom portion of the bag to move upward. Consequently, the resistance at the bottom portion of the bag effectively acts upon the occupant. Therefore, it is possible to provide an airbag which has a more preferable spread form without increasing the output of the inflator.